Welcome to Android Central! Smartwatch phones (i.e, the ones that have a SIM slot, and are not Android Wear devices) are almost always GSM phones, as opposed to CDMA. GSM and CDMA are the two main wireless technologies, with CDMA mostly being in North America (and gradually phasing out). BTC is a GSM network, so you'd just have to make sure the smartwatch phone supports the network bands that BTC uses, which are 850 MHz and 1900 MHz for calls, and 850 MHz for data: BTC : Support